Seven-speed powertrain of an automatic transmission for vehicles

ABSTRACT

Seven forward speeds and three reverse speeds are realized by combining two compound planetary gear sets using three clutches and four brakes, and each shift speed is realized by operating two frictional elements, thereby reducing a capacity of a hydraulic pump and enhancing an efficiency of a hydraulic pressure control by realizing each shift speed by operating two frictional elements. A first shift portion and a second shift portion are disposed on the same shaft axis. The first shift portion includes a first planetary gear set formed as a double pinion planetary gear set and a second planetary gear set formed as a single pinion planetary gear set, and the second shift portion includes a third planetary gear set formed as a single pinion planetary gear set and a fourth planetary gear set formed as a single pinion planetary gear set. The first shift portion is combined by one clutch and two brakes, and the second shift portion is combined by one clutch and two brakes.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2005-0118355 filed in the Korean IntellectualProperty Office on Dec. 6, 2005, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a seven-speed powertrain of anautomatic transmission for vehicles.

(b) Description of the Related Art

Vehicle companies have been developed and adopted different types of apowertrain of an automatic transmission of vehicles, and most ofautomatic transmissions generally used in recent day are a four-speed ora five-speed automatic transmission. Recently, a six-speed automatictransmission has been developed and adopted to a vehicle, and aseven-speed automatic transmission is being developed.

As an example, as shown in FIG. 4 (BENZ 7G-TRONIC seven-speedtransmission), a powertrain is formed to realize seven speeds bycombining two compound planetary gear sets using three clutches, fourbrakes, and one one-way clutch.

In more detail, a first compound planetary gear set 100 is formed bycombining a single pinion planetary gear set and a double pinionplanetary gear set, and a planet carrier 102 and a sun gear 104 areshared, so that the first compound planetary gear set 100 has fouroperational elements of the first sun gear 104, the first planet carrier102, a first ring gear 106, and a second ring gear 108.

In addition, a second compound planetary gear set 110 is formed bycombining two single pinion planetary gear sets, and a third ring gear112 and a fourth planet carrier 114 are directly connected to eachother, so that the second compound planetary gear set 110 has fiveoperational elements of a third sun gear 116, a fourth sun gear 118, athird planet carrier 120, a fourth planet carrier 124, and a fourth ringgear 126.

The first planet carrier 102 is fixedly connected to the fourth ringgear 126 and is connected to a transmission housing 128 via a one-wayclutch F.

The first sun gear 104 is variably connected to the first ring gear 106by a first clutch K1 and is variably fixed to the transmission housing128 by a first brake B1.

The second ring gear 108 is directly connected to an input shaft 130 soas to always act as an input element, and the third ring gear 112 isvariably connected to the input shaft 128 via a second clutch K2.

The third sun gear 116 is variably connected to the fourth sun gear 118via a third clutch K3, and is variably connected to the transmissionhousing 128 via a second brake B2.

The first ring gear 106 and the fourth planet carrier 124 arerespectively variably connected to the transmission housing 128 via athird brake B3 and a fourth brake B4, and the third planet carrier 120is fixedly connected to an output shaft 132 so as to always act as anoutput element.

As shown in FIG. 5, in the above-described seven-speed powertrain, thethird clutch K3, the second brake B2, and the third brake B3 areoperated at a first forward speed; the third clutch K3, the first brakeB1, and the second brake B2 are operated at a second forward speed; thefirst clutch K1, the third clutch K3, and the second brake B2 areoperated at a third forward speed; the first clutch K1, the secondclutch K2, and the second brake B2 are operated at a fourth forwardspeed; the first clutch K1, the second clutch K2, and the third clutchK3 are operated at a fifth forward speed; the second clutch K2, thethird clutch K3, and the first brake B1 are operated at a sixth forwardspeed; and the first clutch K1, the third clutch K3, and the third brakeB3 are operated at a seventh forward speed.

In addition, the third clutch K3, the second brake B2, and the fourthbrake B4 are operated at a first reverse speed; the first clutch K1, thethird clutch K3, and the fourth brake B4 are operated at a secondreverse speeds; and the third clutch K3, the third brake B3, and thefourth brake B4 are operated at a third reverse speed.

However, although the above-described seven-speed power train mayrealize seven forward speeds and three reverse speeds, since sevenfrictional elements and one one-way clutch are needed, the structurebecomes complicated, and an overall length increases.

In addition, since three frictional elements operate at each shiftspeed, an efficiency of a hydraulic pressure control is deteriorated.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to provide aseven-speed powertrain of an automatic transmission for vehiclesrealizing seven forward speeds and three reverse speeds by combining twocompound planetary gear sets using three clutches and four brakes andhaving advantages of having small size and reducing a manufacturingcost.

In addition, the present invention has also been made in an effort toprovide a seven-speed powertrain of an automatic transmission forvehicles having advantages of reducing a capacity of a hydraulic pumpand enhancing an efficiency of a hydraulic pressure control by realizingeach shift speed by operating two frictional elements.

In an exemplary seven-speed powertrain of an automatic transmissionaccording to an embodiment of the present invention, a first shiftportion and a second shift portion are disposed on the same shaft axis,the first shift portion comprising a first planetary gear set formed asa double pinion planetary gear set and a second planetary gear setformed as a single pinion planetary gear set, and the second shiftportion comprising a third planetary gear set formed as a single pinionplanetary gear set and a fourth planetary gear set formed as a singlepinion planetary gear set. The first shift portion is combined by oneclutch and two brakes, so as to realize three forward speeds withrotation power input through an input route from an input shat. Thesecond shift portion is combined by one clutch and two brakes so as torealize seven forward speeds and three reverse speed with rotation powerinput through an input route from the first shift portion and a variableinput route from the input shaft.

Among six operation elements of the first and second planetary gearsets, two pairs of operational elements may be fixedly connected to eachother, so that the first shift portion has a first, a second, a third,and a fourth operational elements, and wherein: the first operationalelement selectively acts as a fixed element; the second operationalelement selectively acts as a fixed element and operates such that thefirst planetary gear set becomes in a direct coupling state; the thirdoperational element always acts as an output element and is variablyconnected to the second operational element such that the firstplanetary gear set becomes in a direct coupling state; and the fourthoperational element always acts as an input element.

In the first shift portion, the first sun gear and the second sun gearmay be directly connected to each other, and the first planet carrierand the second planet carrier may be directly connected to each other,so that the first shift portion comprises a first operational elementformed as the first and second sun gears, a second operational elementformed as the first ring gear, a third operational element formed as thefirst and second planet carriers, and a fourth operational elementformed as the second ring gear.

The first operational element and the second operational element may berespectively connected to a transmission housing via respective brakes,and the second operational element may be connected to the thirdoperational element via a clutch.

Among six operation elements of the third and fourth planetary gearsets, two pairs of operational elements may be fixedly connected to eachother, so that the second shift portion has a fifth, a sixth, a seventh,and an eighth operational elements, and wherein: the fifth operationalelement selectively acts as a fixed element; the sixth operationalelement selectively acts as a fixed element; the seventh operationalelement selectively acts an input element and selectively acts as afixed element; and the eighth operational element acts as an inputelement.

In the second shift portion, the third and fourth sun gears may befixedly connected to each other, and the third ring gear and the fourthplanet carrier may be fixedly connected to each other, so that thesecond shift portion comprises a fifth operational element formed as thethird and fourth sun gears, a sixth operational element formed as thethird planet carrier, a seventh operational element formed as the thirdring gear and the fourth planet carrier, and an eighth operationalelement formed as the fourth ring gear.

The fifth operational element and the seventh operational element may berespectively connected to a transmission housing via respective brakes,and the seventh operational element may be variably connected to aninput shaft via a clutch.

In an exemplary seven-speed powertrain of an automatic transmissionaccording to an embodiment of the present invention, a first shiftportion and a second shift portion are disposed on the same shaft axis,a first shift portion and a second shift portion are disposed on thesame shaft axis and are combined by two clutches and four brakes, thefirst shift portion comprising a first planetary gear set formed as adouble pinion planetary gear set and a second planetary gear set formedas a single pinion planetary gear set, the second shift portioncomprising a third planetary gear set formed as a single pinionplanetary gear set and a fourth planetary gear set formed as a singlepinion planetary gear set. Among six operation elements of the first andsecond planetary gear sets, two pairs of operational elements arefixedly connected to each other, so that the first shift portion has afirst, a second, a third, and a fourth operational elements; the firstoperational element selectively acts as a fixed element; the secondoperational element selectively acts as a fixed element and operatessuch that the first planetary gear set becomes in a direct couplingstate; the third operational element always acts as an output elementand is variably connected to the second operational element such thatthe first planetary gear set becomes in a direct coupling state; and thefourth operational element always acts as an input element. Among sixoperation elements of the third and fourth planetary gear sets, twopairs of operational elements are fixedly connected to each other, sothat the second shift portion has a fifth, a sixth, a seventh, and aneighth operational elements; the fifth operational element selectivelyacts as a fixed element; the sixth operational element selectively actsas a fixed element; the seventh operational element selectively acts aninput element and selectively acts as a fixed element; and the eighthoperational element acts as an input element.

In the first shift portion, the first sun gear and the second sun gearmay be directly connected to each other, and the first planet carrierand the second planet carrier may be directly connected to each other,so that the first shift portion comprises a first operational elementformed as the first and second sun gears, a second operational elementformed as the first ring gear, a third operational element formed as thefirst and second planet carriers, and a fourth operational elementformed as the second ring gear.

The first operational element and the second operational element may berespectively connected to a transmission housing via respective brakes,and the second operational element may be connected to the thirdoperational element via a clutch.

In the second shift portion, the third and fourth sun gears may befixedly connected to each other, and the third ring gear and the fourthplanet carrier may be fixedly connected to each other, so that thesecond shift portion comprises a fifth operational element formed as thethird and fourth sun gears, a sixth operational element formed as thethird planet carrier, a seventh operational element formed as the thirdring gear and the fourth planet carrier, and an eighth operationalelement formed as the fourth ring gear.

The fifth operational element and the seventh operational element may berespectively connected to a transmission housing via respective brakes,and the seventh operational element may be variably connected to aninput shaft via a clutch.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a stick diagram of a powertrain according to an exemplaryembodiment of the present invention.

FIG. 2 is an operational chart of frictional element of a powertrainaccording to an exemplary embodiment of the present invention.

FIG. 3 is a speed diagram by a lever analysis method of a powertrainaccording to an exemplary embodiment of the present invention.

FIG. 4 is a stick diagram of a conventional seven-speed powertrain.

FIG. 5 is an operational chart of frictional element of the powertrainof

DETAILED DESCRIPTION OF THE EMBODIMENTS

An exemplary embodiment of the present invention will hereinafter bedescribed in detail with reference to the accompanying drawings.

Referring to FIG. 1, a powertrain according to an exemplary embodimentof the present invention includes: a first shift portion A including afirst planetary gear set PG1 formed as a double pinion planetary gearset and a second planetary gear set PG2 formed as a single pinionplanetary gear set; a second shift portion B including a third planetarygear set PG3 formed as a single pinion planetary gear set and a fourthplanetary gear set PG4 formed as a single pinion planetary gear set; andtwo clutches C1 and C2 and four brakes B1, B2, B3, and B4.

The first shift portion A and the second shift portion B are disposed onthe same shaft axis line. A first sun gear S1 of the first planetarygear set PG1 and a second sun gear of the second planetary gear set PG2are fixedly connected to each other, and a first planet carrier PC1 anda second planet carrier PC2 are fixedly connected to each other.

Accordingly, the first shift portion A includes a first operationalelement N1 formed as the first and second sun gears S1 and S2, a secondoperational element N2 formed as the first ring gear R1, a thirdoperational element N3 formed as the first and second planet carriersPC1 and PC2, and a fourth operational element N4 formed as the secondring gear R2.

In addition, in the second shift portion B, a third sun gear S3 and afourth sun gear S4 are fixedly connected to each other, and a third ringgear R3 and a fourth planet carrier PC4 are fixedly connected to eachother.

Accordingly, the second shift portion B includes: a fifth operationalelement N5 formed as the third and fourth sun gears S3 and S4; a sixthoperational element N6 formed as a third planet carrier PC3; a seventhoperational element N7 formed as the third ring gear R3 and the fourthplanet carrier PC4; and an eighth operational element N8 formed as thefourth ring gear R4.

The first and second shift portions A and B are combined by a firstclutch C1, a second clutch C2, a first brake B1, a second brake B2, athird brake B3, and a fourth brake B4, so that the first shift portionoutputs forward three speed such as a reduced speed and the same speed,and the second shift portion B outputs forward seven speeds and reversethree speeds using power input from the first shift portion A androtation power input from an input shaft IS.

For such operations, the first operational element N1 is variablyconnected to a transmission housing H via the second brake B2 interposedtherebetween so as to act as a selective fixed element.

The second operational element N2 is variably connected to the thirdoperational element N3 via the second clutch C2 interposed therebetween,and the second operational element N3 is connected to the transmissionhousing H via the first brake B1 interposed therebetween so as toselectively act as a fixed element.

The third operational element N3 is fixedly connected to the eighthoperational element N8 so as to act as an output element of the firstshift portion A and is connected to the transmission housing H via thefirst brake B1 interposed therebetween so as to selectively acts as afixed element.

The fourth operational element N4 is directly connected to the inputshaft IS receiving rotation power from a torque converter TC so as toalways act as an input element.

The fifth operational element N5 is connected to the transmissionhousing H via the third brake B3 interposed therebetween so as to act asa selective fixed element.

The sixth operational element N6 is connected to an output shaft OS soas to always act as an output element.

The seventh operational element N7 is connected to the input shaft ISvia the first clutch C1 interposed therebetween so as to act as aselective input element and is connected to the transmission housing Hvia the fourth brake B4 interposed therebetween so as to act as aselective fixed element.

The eighth operational element N8 is connected to the third operationalelement N3 so as to act as an input element always receiving poweroutput from the first shift portion A.

The above-described powertrain according to an embodiment of the presentinvention can realize seven forward speeds and three reverse speeds byoperating frictional elements as shown in FIG. 2.

FIG. 3 is a speed diagram by a lever analysis method of a powertrainaccording to an exemplary embodiment of the present invention. Positionsof the operational elements on the speed diagram are determined byconnections of the planetary gear set, and this is well known in the artso further detailed explanations will be omitted.

That is, at the first forward speed, the first brake B1 of the firstshift portion A and the third brake B3 of the second shift portion B areoperated.

Accordingly, in the first shift portion A, the second operationalelement N2 acts as a fixed element by an operation of the first brake B1and an input is performed through the fourth operational element N4, sothat reduced power is output through the third operational element N3that is an output element.

If the reduced rotation power output from the first shift portion A isinput to the second shift portion B through the eighth operationalelement N8, the fifth operational element N5 acts as a fixed elementsince the third brake B3 operates and the reduced rotation power isoutput through the sixth operational element N6, so that the firstforward speed that is the lowest shift speed is realized (referring toD1 in FIG. 3).

If a vehicle speed is increased in a control state of the first forwardspeed, a transmission control unit controls the operation of the firstbrake B1 of the first shift portion A to be released from the controlstate of the first forward speed and controls the second brake B2 to beoperated.

Then, a fixed element of the first shift portion A is changed to thefirst operational element N1, so the rotation power is reduced to aspeed higher than the first forward speed. The reduced power is outputthrough the third operational element N3 and is then input to the eighthoperational element N8 of the second shift portion B.

If the reduced power output from the first shift portion A is input tothe second shift portion B through the eighth operational element N8,the second shift portion B reduces the input power, which is higher thanthe input power at the first forward speed, with the same reductionratio as the first forward speed and outputs the reduced power since thesecond shift portion B is controlled in the same manner as the firstforward speed, so that the second forward speed is realized (referringto D2 of FIG. 3).

If a vehicle speed is increased in a control state of the second forwardspeed, a transmission control unit controls the operation of the secondbrake B2 of the first shift portion A to be released from the controlstate of the second forward speed and controls the second clutch C2 ofthe first shift portion A to be operated.

Accordingly, since the first operational element N1 and the secondoperational element N2 of the first shift portion A are fixedlyconnected to each other by the operation of the second clutch C2 and thefirst planetary gear set PG1 thereby becomes a direct coupling state,the whole portion of the first shift portion A becomes a direct couplingstate so that input power is output through the third operationalelement N3 of the first shift portion A without speed change and thepower output from the first shift portion A is input to the eighthoperational element N8 of the second shift portion B.

If the rotation power of the same speed with the original input is inputto the second shift portion B through the eighth operational element N8,the second shift portion B reduces the input power, which is higher thanthe input power at the second forward speed, with the same reductionratio as the second forward speed and outputs the reduced power sincethe second shift portion B is controlled in the same manner as the firstand second forward speeds, so that the third forward speed is realized(referring to D3 of FIG. 3).

If a vehicle speed is increased in a control state of the third forwardspeed, a transmission control unit controls the operation of the secondclutch C2 of the first shift portion A to be released from the controlstate of the third forward speed and controls the first clutch C1 of thesecond shift portion B to be operated. Since no frictional element ofthe first shift portion A operates, the first shift portion A has noeffect on speed shifting. In the second shift portion B, rotation poweris input through the seventh operational element N7 by the operation ofthe first clutch C1, and the fifth operational element N5 acts as afixed element the operation of the third brake B3.

Accordingly, output speed becomes higher than that of the third forwardspeed and thereby the fourth forward speed is realized (referring to D4of FIG. 3).

If a vehicle speed is increased in a control state of the fourth forwardspeed, a transmission control unit controls the operation of the thirdbrake B3 of the second shift portion B to be released from the controlstate of the fourth forward speed and controls the second clutch C2 ofthe first shift portion A to be operated.

Since the first planetary gear set PG1 of the first shift portion Abecomes in a direct coupling state just as at the third forward speed bythe operation of the second clutch C2, the whole portion of the firstshift portion A becomes a direct coupling state so that input power isoutput through the third operational element N3 of the first shiftportion A without speed change and the power output from the first shiftportion A is input to the eighth operational element N8 of the secondshift portion B.

In addition, since rotation power is input to the second shift portion Bby the operation of the first clutch C1, rotation power input to thesecond shift portion B is performed through two routes. Accordingly, thewhole portion of the second shift portion becomes a direct couplingstate, so that the fifth forward speed in which the input is outputwithout speed change is realized (referring to D5 of FIG. 3).

If a vehicle speed is increased in a control state of the fifth forwardspeed, a transmission control unit controls the operation of the secondclutch C2 of the first shift portion A to be released from the controlstate of the fifth forward speed and controls the second brake B2 of thefirst shift portion A to be operated.

Since in the first shift portion A the first operational element N1 actsas a fixed element in a state that power is input through the fourthoperational element N4, the rotation power is reduced at the same ratioas the second forward speed and is output through the third operationalelement N3. The reduced power output from the first shift portion A isinput through the eighth operational element N8 of the second shiftportion B.

If the reduced rotation power is input to the second shift portion Bthrough the eighth operational element N8 from the first shift portionA, since in the second shift portion B rotation power is input throughthe eighth operational element N8 in a state that rotation power of theinput shaft IS is input through the seventh operational element N7 bythe operation of the first clutch C1, rotation power having higher speedthan rotation power input through the seventh operational element N7 isoutput by cooperation of these input powers, so that the sixth forwardspeed outputting increased rotation power is realized (referring to D6of FIG. 3).

If a vehicle speed is increased in a control state of the sixth forwardspeed, a transmission control unit controls the operation of the secondclutch C2 of the first shift portion A to be released from the controlstate of the sixth forward speed and controls the first brake B1 of thefirst shift portion A to be operated.

Then, since in the first shift portion A the second operational elementN2 acts as a fixed element in a state that rotation power is inputthrough the fourth operational element N4, the rotation power is reducedwith a reduction ratio greater than that in the sixth forward speed andthe reduced power is output through the third operational element N3,and the power output from the first shift portion A is input through theeighth operational element N8 of the second shift portion B.

In the reduced rotation power is input to the second shift portion Bthrough the eighth operational element N8 from the first shift portionA, since in the second shift portion B the rotation power reduced with areduction ratio greater than that in the sixth forward speed is inputthrough the eighth operational element N8 in a state that the rotationpower of the input shaft IS is input through the seventh operationalelement N7 by the operation of the first clutch C1, rotation powerhaving higher speed than rotation power input through the seventhoperational element N7 is output by cooperation of these input powers,so that the seventh forward speed outputting increased rotation powermore than the sixth forward speed is realized (referring to D7 of FIG.3).

At the first reverse speed, the first brake B1 of the first shiftportion A and the fourth brake B4 of the second shift portion B arecontrolled to be operated.

Then, since in the first shift portion A rotation power is input throughthe forth operational element N4 in a state that the second operationalelement N2 acts as a fixed element by the operation of the first brakeB1, reduced rotation power is output through the third operationalelement N3 that is an output element, and rotation power is inputthrough the eighth operational element N8 of the second shift portion B.

If the reduced rotation power is input to the second shift portion Bthrough the eighth operational element N8 from the first shift portionA, since the fourth brake B4 in the second shift portion B operates, theseventh operational element N7 acts as a fixed element and reducedrotation power in a reverse direction is output through the sixthoperational element N6, so that the first reverse speed is realized(referring to R1 of FIG. 3).

If a vehicle speed is increased in a control state of the first reversespeed, a transmission control unit controls the operation of the firstbrake B1 of the first shift portion A to be released from the controlstate of the first reverse speed and controls the second brake B2 of thefirst shift portion A to be operated.

Accordingly, in the first shift portion A, the fixed element is changedto the first operational element N1, and rotation power is reduced at aspeed a little bit higher than the first reverse speed. The reducedoutput power is output through the third operational element N3, and therotation power output from the first shift portion A is input throughthe eighth operational element N8 of the second shift portion B.

If the reduced rotation power is input to the second shift portion Bthrough the eighth operational element N8 from the first shift portionA, since the second shift portion B is controlled in the same way as thefirst reverse speed, the rotation power with a higher speed than thefirst reverse speed is reduced with the same reduction ratio as thefirst reverse speed and the reduced power is output, so that the secondreverse speed is realized (referring to R2 of FIG. 3).

If a vehicle speed is increased in a control state of the second reversespeed, a transmission control unit controls the operation of the secondbrake B2 of the first shift portion A to be released from the controlstate of the second reverse speed and controls the second clutch C2 ofthe first shift portion A to be operated.

Accordingly, since in the first shift portion A the first planetary gearset PG1 becomes in a direct coupling state by the operation of thesecond clutch C2, the whole portion of the first shift portion A becomesin a direct coupling state so that input rotation power is outputthrough the third operational element N3 without speed change, and thepower output from the first shift portion A is input through the eighthoperational element N8 of the second shift portion B.

If the rotation power of the same speed as the original input is inputto the second shift portion B through the eighth operational element N8from the first shift portion A, since the second shift portion B iscontrolled in the same way as the first and second reverse speeds,rotation power of a higher speed than the second reverse speed isreduced with the same reduction ratio as the second reverse speed, andthe reduced power is output, so that the third reverse speed is realized(referring to R3 of FIG. 3).

According to the present invention, since two compound planetary gearsets are disposed on the same shaft axis line and the compound planetarygear set thereof are combined by two clutches and four brakes so as torealize seven forward speeds and three reverse speeds, an overall sizeof a transmission can be substantially decreased and a manufacturingcost can also be reduced.

In addition, since each shift speed is realized by the operation of twofrictional elements, a capacity of a hydraulic pump can be reduced andan efficiency of a hydraulic pressure control can be enhanced.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A seven-speed powertrain of an automatic transmission for vehicles,wherein a first shift portion and a second shift portion are disposed onthe same shaft axis, the first shift portion comprising a firstplanetary gear set formed as a double pinion planetary gear set and asecond planetary gear set formed as a single pinion planetary gear set,and the second shift portion comprising a third planetary gear setformed as a single pinion planetary gear set and a fourth planetary gearset formed as a single pinion planetary gear set, and wherein: the firstshift portion is combined by one clutch and two brakes, so as to realizethree forward speeds with rotation power input through an input routefrom an input shaft; and the second shift portion is combined by oneclutch and two brakes so as to realize seven forward speeds and threereverse speed with rotation power input through an input route from thefirst shift portion and a variable input route from the input shaft. 2.The seven-speed powertrain of claim 1, wherein, among six operationelements of the first and second planetary gear sets, two pairs ofoperational elements are fixedly connected to each other, so that thefirst shift portion has a first, a second, a third, and a fourthoperational elements, and wherein: the first operational elementselectively acts as a fixed element; the second operational elementselectively acts as a fixed element and operates such that the firstplanetary gear set becomes in a direct coupling state; the thirdoperational element always acts as an output element and is variablyconnected to the second operational element such that the firstplanetary gear set becomes in a direct coupling state; and the fourthoperational element always acts as an input element.
 3. The seven-speedpowertrain of claim 1, wherein, in the first shift portion, the firstsun gear and the second sun gear are directly connected to each other,and the first planet carrier and the second planet carrier are directlyconnected to each other, so that the first shift portion comprises afirst operational element formed as the first and second sun gears, asecond operational element formed as the first ring gear, a thirdoperational element formed as the first and second planet carriers, anda fourth operational element formed as the second ring gear.
 4. Theseven-speed powertrain of claim 2, wherein: the first operationalelement and the second operational element are respectively connected toa transmission housing via respective brakes; and the second operationalelement is connected to the third operational element via a clutch. 5.The seven-speed powertrain of claim 1, wherein, among six operationelements of the third and fourth planetary gear sets, two pairs ofoperational elements are fixedly connected to each other, so that thesecond shift portion has a fifth, a sixth, a seventh, and an eighthoperational elements, and wherein: the fifth operational elementselectively acts as a fixed element; the sixth operational elementselectively acts as a fixed element; the seventh operational elementselectively acts an input element and selectively acts as a fixedelement; and the eighth operational element acts as an input element. 6.The seven-speed powertrain of claim 1, wherein, in the second shiftportion, the third and fourth sun gears are fixedly connected to eachother, and the third ring gear and the fourth planet carrier are fixedlyconnected to each other, so that the second shift portion comprises afifth operational element formed as the third and fourth sun gears, asixth operational element formed as the third planet carrier, a seventhoperational element formed as the third ring gear and the fourth planetcarrier, and an eighth operational element formed as the fourth ringgear.
 7. The seven-speed powertrain of claim 5, wherein: the fifthoperational element and the seventh operational element are respectivelyconnected to a transmission housing via respective brakes; and theseventh operational element is variably connected to an input shaft viaa clutch.
 8. A seven-speed powertrain of an automatic transmission forvehicles, wherein a first shift portion and a second shift portion aredisposed on the same shaft axis and are combined by two clutches andfour brakes, the first shift portion comprising a first planetary gearset formed as a double pinion planetary gear set and a second planetarygear set formed as a single pinion planetary gear set, the second shiftportion comprising a third planetary gear set formed as a single pinionplanetary gear set and a fourth planetary gear set formed as a singlepinion planetary gear set, and wherein: among six operation elements ofthe first and second planetary gear sets, two pairs of operationalelements are fixedly connected to each other, so that the first shiftportion has a first, a second, a third, and a fourth operationalelements; the first operational element selectively acts as a fixedelement; the second operational element selectively acts as a fixedelement and operates such that the first planetary gear set becomes in adirect coupling state; the third operational element always acts as anoutput element and is variably connected to the second operationalelement such that the first planetary gear set becomes in a directcoupling state; and the fourth operational element always acts as aninput element, and wherein: among six operation elements of the thirdand fourth planetary gear sets, two pairs of operational elements arefixedly connected to each other, so that the second shift portion has afifth, a sixth, a seventh, and an eighth operational elements; the fifthoperational element selectively acts as a fixed element; the sixthoperational element selectively acts as a fixed element; the seventhoperational element selectively acts an input element and selectivelyacts as a fixed element; and the eighth operational element acts as aninput element.
 9. The seven-speed powertrain of claim 8, wherein, in thefirst shift portion, the first sun gear and the second sun gear aredirectly connected to each other, and the first planet carrier and thesecond planet carrier are directly connected to each other, so that thefirst shift portion comprises a first operational element formed as thefirst and second sun gears, a second operational element formed as thefirst ring gear, a third operational element formed as the first andsecond planet carriers, and a fourth operational element formed as thesecond ring gear.
 10. The seven-speed powertrain of claim 8, wherein:the first operational element and the second operational element arerespectively connected to a transmission housing via respective brakes;and the second operational element is connected to the third operationalelement via a clutch.
 11. The seven-speed powertrain of claim 8,wherein, in the second shift portion, the third and fourth sun gears arefixedly connected to each other, and the third ring gear and the fourthplanet carrier are fixedly connected to each other, so that the secondshift portion comprises a fifth operational element formed as the thirdand fourth sun gears, a sixth operational element formed as the thirdplanet carrier, a seventh operational element formed as the third ringgear and the fourth planet carrier, and an eighth operational elementformed as the fourth ring gear.
 12. The seven-speed powertrain of claim8, wherein: the fifth operational element and the seventh operationalelement are respectively connected to a transmission housing viarespective brakes; and the seventh operational element is variablyconnected to an input shaft via a clutch.